how not cold is "not cold?" Is it cool, but not cold or not cold at all? If the air is cool but not cold, maybe it is just the microfilter. If the air is not cold, you obviously have a leak somewhere in the system (eveporator core, condenser, hoses, etc.) and have lost your refrigerant. I seriously doubt just cleaning the microfilter will aleviate your problem, but it certainly doesn't hurt to try.